MUMBAI, May 12 (Reuters) - Almost two-thirds of the drug combinations widely sold in India to fight pain, depression, and psychotic conditions lack the necessary regulatory approvals, despite some of the pills being banned internationally, a study published on Tuesday shows.

India's reputation as a reliable supplier of cheap generic medicines has taken a hit after sanctions by the United States and Britain faced by some of its largest drugmakers over violations of standard drug-making practices.

Thousands of fixed-dose combination drugs (FDCs), or cocktails of two or more medicines, are sold in India. While many are safe and effective, including those used to treat HIV and tuberculosis, others have been found unsafe and even dangerous, said the researchers who ran the study.

"Unapproved formulations should be banned immediately, prioritizing those withdrawn or banned internationally, and undertaking a review of benefits and risks for patients," the researchers said.

Just 60 of the 175 pain, depression, anti-psychotic and diabetes FDC formulations sold in India between 2007 and 2012 had approval from the central government drugs regulator, they found.

Also unapproved were 90 of the 124 painkiller combinations evaluated.

The study results were published in the Public Library of Science journal, PLOS Medicine.

FDC formulations marketed in India despite being withdrawn or restricted internationally include painkillers such as nimesulide, thiocolchicoside, dextropropoxyphene and metamizole, the study said.

Both domestic and international drug companies sell FDCs in India.

Indian law requires central government regulatory approval of all new drugs, including FDCs, but many FDCs have come to market on the basis of approval from individual state regulators, a parliamentary panel said in 2012.

Although the panel cited "ambiguity" about the states' licensing powers until May 2002, the researchers said they found no evidence of that.

India has legally required central government regulators' approval of all new drugs, including FDCs, since 1961.

FDCs made up a growing volume of total sales during the period studied, accounting for more than half of all pain and oral anti-diabetic drug sales by 2011-2012. (Reporting by Zeba Siddiqui in Mumbai; Editing by Clarence Fernandez)